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Main modwrt.png

Modbus RTU to Emoncms Thingspeak

Modbus to Emoncms. The ModWRT is a Modbus RTU unit to interface with one or several RS485 RTU devices. The ModWRT sends a predefined set of registers value to a server for data logging and display.
The end server can be either of type Emoncms, Thingspeak, InitialState or another custom server.

All communication and dataflow parameters are configured using a web interface.

Technical Specifications

  • RS485 port
  • Ethernet port
  • Integrated Wifi
  • Micro-usb Power supply
  • Operating system: OpenWRT 14.07
  • Flash Memory: 64MB
  • Dimensions: 90x60x30mm
  • Enclosure: Aluminium case
  • Optional Wifi antenna


The ModWRT web interface is build within the OpenWRT web interface.

There are three main functional area which are:
1/ RTU's definitions
2/ Servers definitions
3/ Dataflow configuration (ie which data goes where).

1. RTU definition

All Modbus RTU devices can be configured on one single page using Slave ID and communication parameters (baud rate etc).

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2. Servers definition

Internet of Thing (iot) servers can be configured on this page.

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Name: Server identification name.
Type: Type of target server. Can be one of Emoncms, Thingspeak or InitialState.
Hostname: Hostname or IP address of the server. Can be local or on www.
Apikey: APikey for identification with target server.

3. Dataflow Configuration

This page will configure all dataflow combination.

A single dataflow can query different RTU unit to send combined data onto a single export.

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Description: Optional. A description relevant to the user.
Enabled: Enable/Disable the dataflow.
ID: ID for the receiving server.
Server: Previously defined target server.
Channel Name: Optional. A name relevant to the user.
Rtu: The RTU ID defined previously.
Datatype: The datatype to interpret the receiving data. Must be one of int, float, floatABCD, floatDCBA, floatCDAB, floatBADC.
Register: Starting register on the RTU unit for the requested data. Note the length is managed by previous field datatype. Decimal format required.

As an example the above example will display the following data on Emoncms.

Web 004.png